Coronary insufficiency goes the opposite direction (pale, gray)...
If he did die from Cyanide poisoning, it should be an easy thing to find from toxicology tests.
A likely form is Potassium cyanide (KCN), because of its water solubility. It works by shutting down the respiratory system by preventing oxygen from being absorbed from the blood. This causes the reddish hue of the complexion. Death occurs from the deprivation of oxygen to the neural tissues (histotoxic hypoxia). It is the same effect as carbon monoxide poisoning. And the over consumption of alcohal is another similar effect. The brain and the heart are the most sensitive areas affected by oxygen deprivation. Most important, Potassium cyanide poisoning very closely mimics a heart attack. The only symptom that may identify Potassium cyanide poisoning as the cause is the signs of convulsions just before coma and death.
Potassium cyanide is the most common type of suicide poison. The Jim Jones People’s Temple Kool Aid and the Heaven’s Gate suicides are examples of Potassium cyanide poisoning. The suicide pills of the Nazis are also an example.
An autopsy would reveal the smell of bitter almonds and unmistaken blue color of the mucosa of the stomach. Such is the result of ferric iron in the form of ferric hydroxide (Fe(OH)3))being unmasked from compounds such as haemosiderin by acid in the stomach. The ferric iron then reacts with a ferrocyanide (nitroprusside) to produce an insoluble blue compound, ferric ferrocyanide.